Wide angle objective

ABSTRACT

This disclosure relates to a Wide Angle Lens of the retrofocus type having a new lens group arrangement which comprises from the object end to the image end a first negative group, a second negative group in the form of a meniscus having a concave image side surface, a third positive group having a convex object side surface, a fourth positive group having a convex image side surface, a fifth negative group, and a sixth positive group having convex image and object side surfaces.

This application is a continuation-in-part of co-pending application Ser. No. 392,118 filed Aug. 27, 1973, now abandoned.

This invention relates to lenses, and more particularly to those known as wide angle lenses of the retrofocus type.

Wide angle lenses may be defined as those in which the diameter of the film or image frame of the camera with which the lens is used is substantially equal to or greater than the equivalent focal length of the lens. Moderately wide angle rectrofocus objectives covering field angles of approximately 80° have been known for many years. Typically these lenses have been large in length and diameter resulting in considerable manufacturing expense and a lack of portability. In order to reduce the size, it is necessary to increase the lens element powers which normally increase the lens surface aberration contributions. When wide angle objectives of reduced size configuration are constricted to relative apertures of f/2.8, the need to correct large aperture dependence aberrations is apparent; however, when relative apertures of approximately f/2.0 or greater are desired, the amount of zonal spherical aberration and aperture dependent coma is considerably increased. Moreover, due to the large lens element powers, the amount of field curvature of third order and greater becomes excessive. Even though the aperture dependent aberrations may be well corrected, the zonal field curvature and astigmatism will severely limit resolution.

The present invention provides a new and improved lens configuration for wide angle objectives through the employment of a new lens grouping arrangement which minimizes the lens element powers in order to obtain the necessary back focal distance and front vertex distance as required to be useful in single lens reflex cameras. The minimization of the lens group powers decreases the surface contributions to distortion and various aberrations.

Briefly stated, a wide angle lens embodying the invention comprises a first lens group from the object end to the image end which is afocal, a second diverging group, third and fourth converging groups, a fifth diverging group and a sixth converging group. The lens groups and elements, and particularly the fourth group, have relative powers and configurations to achieve the objects of the invention, as hereinafter more specifically pointed out.

An object of this invention is to provide a new and improved wide angle lens of the retrofocus type.

Another object of this invention is to provide a lens of the type described of large relative aperture with minimized field curvature and astigmatism.

A further object of this invention is the provision of a lens of the type described having the capability of focusing to very close object distance without introduction of unacceptable field curvature and astigmatism.

The features of the invention which are believed to be novel are particularly pointed out and distinctly claimed in the concluding portion of this specification. However, the invention both as to its organization and operation, together with further objects and advantages thereof, may best be appreciated by reference to the following detailed description taken in conjunction with the drawings, wherein:

Figs. 1 - 3 are side elevations of lens embodying the invention;

FIGS. 4 and 5 are curves illustrating the improved performance of the lens of FIG. 1;

FIGS. 6 - 10 are side elevations of additional lens embodying the invention; and

FIGS. 11 and 12 are curves illustrating the improved performance of the lens of FIG. 8.

In all lens designs, the elemental groupings and spacings thereof are chosen to minimize aberrations and distortion of the overall lens and generally provide a true image of an object. The lens groupings are chosen to provide a lens of given field angle or equivalent focal length for a specified image quality. Therefore, the contribution of each lens group or element in multi-element lens is incapable of precise definition inasmuch as all lens configurations are selected in view of the others to provide the desired result.

The objects of the present invention are achieved by the provision of a new grouping of lens elements as hereinafter described.

A lens embodying the invention as disclosed comprises six lens groups from the object end to the image end as follows:

I. a two element group of negative power.

Ii. a meniscus of negative power.

Iii. a positive element having a convex front surface.

Iv. a positive element or doublet having a concave front surface and a convex rear surface.

V. a meniscus of negative power, and

Vi. a positive doublet.

A first lens 10 embodying the invention is set forth in FIG. 1, and comprises nine lens elements L1 - L9, arranged in six lens groups. The surfaces of the elements L1 - L9 are defined in radii R1 - R16 as shown. The first group viewed from the object end to the image end comprises elements L1 and L2 which are, as a combination, afocal with respect to the equivalent focal length (EFL) of the overall lens. The second group II is comprised of a meniscus L3 of negative power (diverging). The third group III is comprised of a biconvex element L4 of positive power (converging). The fourth group IV is comprised of a contacting doublet L5 and L6 of positive power (converging). The fifth group V is comprised of a negative meniscus (diverging) and the sixth group VI is a contacting doublet of positive power (diverging). This lens is defined by the data set forth in Table I.

A second lens 11 embodying the invention is set forth in FIG. 2 and comprises lens elements L1 - L8, arranged in six groups of the same relative powers as the lens of FIG. 1. Lens 11 differs from lens 10 primarily in that Group IV comprises a single element L5, but which is still of positive power (converging). Lens 11 is defined by the data set forth in Table II.

Another lens 12 is shown in FIG. 3 and comprises the six group I - VI of the same relative power as lens 11, having eight elements L1 - L8. The lens surfaces are defined on radii R1 - R15 as shown. Lens 12 differs from lens 11 primarily in that Group VI, elements L7 and L8, is comprised of a meniscus and a contacting bi-convex element in that order, rather than vice-versa, as lens 11. Lens 12 is defined by the data as set forth in Table III.

In the tables the index of refraction is denoted as N_(d) and the dispersion as referenced by the Abbe number is denoted by V_(d).

Table I sets forth data on lens 10 of FIG. 1 scaled to an EFL of 28.7mm for a 24 × 36mm image frame, and having a relative aperture of F/1.9.

                  TABLE I                                                          ______________________________________                                         FIG. 1                                                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       38.387mm                                                         L1                     2.435mm       1.5168                                                                              64.2                                      R2     18.755                                                                                    8.5083                                                       R3     -119.389                                                           L2                     7.167         1.7995                                                                              42.3                                      R4     -52.877                                                                                   4.72-0.20                                                    R5     18.178                                                             L3                     2.180         1.5831                                                                              59.5                                      R6     12.456                                                                                    9.369                                                        R7     49.0379                                                            L4                     2.159         1.8306                                                                              36.5                                      R8     -123.776                                                                                  2.581                                                        R9     -22.141                                                            L5                     6.000         1.7470                                                                              27.5                                      R10    -109.562                                                           L6                     5.774         1.7620                                                                              40.3                                      R11    -21.131                                                                                   0.135                                                        R12    55.725                                                             L7                     2.454         1.8467                                                                              23.8                                      R13    26.386                                                                                    2.239                                                        R14    76.751                                                             L8                     6.000         1.8042                                                                              46.5                                      R15    -22.374                                                            L9                     1.500         1.8052                                                                              25.5                                      R16    -54.363                                                            ______________________________________                                          BFL = 38.8mm                                                                   The aperture stop is located 8.4mm after L3.                                   The spacing between elements L2 and L3 varies from 0.20mm to 4.72mm for        focusing from infinity to 178.4mm. Elements L3 - L9 move in fixed relatio      as a group during focusing travel.                                       

Table II sets forth data on lens 11 of FIG. 2 scaled to an EFL of 28.7mm for a 24 × 36mm image frame, and having a relative aperture of F/2.0.

                  TABLE II                                                         ______________________________________                                         FIG. 2                                                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                                   R1       38.570mm                                                         L1                       2.435mm     1.5168                                                                              64.2                                      R2     19.187                                                                                    8.508                                                        R3     -118.121                                                           L2                     4.797         1.7995                                                                              42.3                                      R4     -53.498                                                                                      4.000-0.25                                                R5     18.556                                                             L3                     2.180         1.5831                                                                              59.5                                      R6     12.336                                                                                    10.615                                                       R7     50.120                                                             L4                     2.159         1.8306                                                                              36.5                                      R8     -160.5232                                                                                 2.581                                                        R9     -22.590                                                            L5                     10.883        1.7600                                                                              47.5                                      R10    -21.050                                                                                   0.135                                                        R11    51.8954                                                            L6                     3.257         1.8467                                                                              23.8                                      R12    26.298                                                                                    2.239                                                        R13    77.064                                                             L7                     7.000         1.8042                                                                              46.5                                      R14    -18.570                                                            L8                     1.500         1.8052                                                                              25.5                                      R15    -51.214                                                            ______________________________________                                          BFL = 39.0mm                                                                   The aperture stop is located 9.55mm behind L3 Elements L3 - L8 move in         fixed relation as a group for focusing while L1 and L2 are stationary. Th      spacing between elements L2 and L3 varies from 0.25mm to 4.00mm for            focusing from infinity to 178mm.                                         

Table III sets forth data on lens 12 of FIG. 3 scaled to an EFL of 28.7mm for a 24×36mm image frame and having a relative aperture of F/2.0.

                  TABLE III                                                        ______________________________________                                         FIG. 3                                                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       39.897mm                                                         L1                       2.435mm     1.520                                                                               65.6                                      R2     19.832                                                                                    8.500                                                        R3     -111.180                                                           L2                     5.835         1.802                                                                               47.5                                      R4     -55.111                                                                                      4.000-0.25                                                R5     17.557                                                             L3                     2.180         1.807                                                                               44.3                                      R6     2.193                                                                                     10.789                                                       R7     47.013                                                             L4                     2.433         1.833                                                                               41.8                                      R8     -138.976                                                                                  3.390                                                        R9     -23.286                                                            L5                     9.700         1.837                                                                               51.9                                      R10    -21.573                                                                                   0.135                                                        R11    51.904                                                             L6                     3.324         1.848                                                                               23.4                                      R12    26.009                                                                                    2.682                                                        R13    85.346                                                             L7                     1.000         1.848                                                                               23.4                                      R14    31.429                                                             L8                     4.000         1.776                                                                               50.6                                      R15    -43.746                                                            ______________________________________                                          BFL = 39.9mm                                                                   The aperture stop is located 10.79mm behind L3. The spacing between            elements L2 and L3 varies between 0.25mm and 4.00mm for focusing from          inifinity to 178mm. Elements L3 - L8 move in fixed relation as a group fo      focusing while L1 and L2 are stationary.                                 

In the examples of Tables I - III, all lens have a rated EFL of 28mm and a rated equivalent aperture of F/1.9, as scaled to a film or image frame size of 24 × 36mm. The lenses may, of course, be scaled to other image frame sizes, and EFL's.

FIGS. 4 and 5 exemplify plots of image height versus focal plane shift for the lens of FIG. 1, and a known wide angle lens scaled to 28mm EFL and a stated relative aperture of F/2.0, respectively, as shown in U.S. Pat. No. 3,736,049. Comparisons were made at a magnification of M = - 0.025 for a half image height of 20mm, for both sagittal S and tangential T rays.

The curves of FIG. 4 are relatively close together evidencing essential elimination of astigmatism. The curves of FIG. 4 have less deviation from the vertical, and are generally flatter than those of FIG. 5, to evidence a substantial reduction in field curvature.

The lenses of Tables I, II and III are designed for the first group elements L1 and L2 to be stationary while the rear elements are shifted in fixed relation as a group for focusing, as disclosed and claimed in the copending application of John A. Lawson, Ser. No. 492,413, filed July 29, 1974.

However, the lens Groups may also be arranged to move differentially as in the conventional wide angle objectives. For example, the entire objective may be shifted for focusing, while the fourth and fifth lens Groups move differentially in a well known manner. Also, the lens may be arranged to move only Groups V and VI for focusing, as disclosed and claimed in U.S. Pat. No. 3,975,090.

Further examples of lenses embodying the invention are set forth in FIGS. 6 - 10, and Tables IV - IX. In all of the examples, Group IV is an air spaced doublet L5, L6.

Table IV sets forth data on the lens 13 of FIG. 6 as scaled to an EFL of 28.5mm for a 24 × 36mm image plane, and having a relative aperture of F/1.9.

                  TABLE IV                                                         ______________________________________                                         FIG. 6                                                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     155.101                                                            L1                     4.160         1.562                                                                               58.52                                     R2     -541.744                                                                                   .300                                                        R3     29.242                                                             L2                     3.000         1.487                                                                               70.4                                      R4     13.031                                                                                    12.759                                                       R5     22.898                                                             L3                     2.000         1.800                                                                               42.3                                      R6     15.520                                                                                    8.692                                                        R7     48.249                                                             L4                     3.200         1.785                                                                               25.7                                      R8     -70.561                                                                                   1.967                                                        R9     -24.204                                                            L5                     2.164         1.805                                                                               25.5                                      R10    -1430.264                                                                                  .844                                                        R11    -94.529                                                            L6                     5.504         1.800                                                                               42.3                                      R12    -19.767                                                                                       3.550-1.028                                              R13    45.215                                                             L7                     2.580         1.847                                                                               23.8                                      R14    29.179                                                                                    1.700                                                        R15    70.687                                                             L8                     8.00          1.743                                                                               49.2                                      R16    -19.969                                                            L9                     2.700         1.847                                                                               23.8                                      R17    -44.577                                                            ______________________________________                                          The aperture stop is located 7.18mm after L3. The BFL varies from 39.68mm      to 44.34mm as the lens is focused from infinity to an object distance of       174.7mm. All lens elements move for focusing and the space between Groups      IV and V moves differentially as shown.                                  

Table V sets forth data on a lens 14 substantially as shown in FIG. 7 scaled to an EFL of 28.6mm for a 24 × 36mm frame size and a relative aperture of F/1.9.

                  TABLE V                                                          ______________________________________                                         FIG. 7                                                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     42.160                                                             L1                     5.700         1.487                                                                               70.4                                      R2     384.104                                                                                    .300                                                        R3     35.935                                                             L2                     2.800         1.487                                                                               70.4                                      R4     11.488                                                                                    4.032                                                        R5     26.721                                                             L3                     2.000         1.517                                                                               64.2                                      R6     15.510                                                                                    14.343                                                       R7     39.692                                                             L4                     3.200         1.689                                                                               31.2                                      R8     925.392                                                                                   2.973                                                        R9     -76.847                                                            L5                     2.164         1.847                                                                               23.8                                      R10    97.091                                                                                    1.750                                                        R11    -75.162                                                            L6                     4.549         1.800                                                                               42.3                                      R12    -21.352                                                                                      4.098-.100                                                R13    37.634                                                             L7                     2.700         1.722                                                                               29.2                                      R14    32.248                                                                                    2.000                                                        R15    70.613                                                             L8                     8.400         1.641                                                                               59.8                                      R16    -18.940                                                            L9                     2.700         1.805                                                                               25.5                                      R17    -42.358                                                            ______________________________________                                          The aperture stop is located 12.3mm after L3. The BFL varies from 39.2mm       to 43.2mm as the lens is focused from infinity to an object distance of        203mm. Groups I-IV are stationary while Groups V and VI (elements L7-L9)       move in fixed relation for focusing.                                     

Table VI sets forth data on lens 15 of FIG. 8 scaled to an EFL of 35.0mm for a 24 × 36mm image frame, and a relative aperture of F/2.0.

                  TABLE VI                                                         ______________________________________                                         FIG. 8                                                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     31.195                                                             L1                     2.998         1.517                                                                               64.2                                      R2     20.569                                                                                    7.074                                                        R3     -96.642                                                            L2                     2.829         1.785                                                                               25.7                                      R4     -58.277                                                                                   0.726                                                        R5     18.356                                                             L3                     4.321         1.723                                                                               38.0                                      R6     12.649                                                                                    11.925                                                       R7     53.996                                                             L4                     2.800         1.831                                                                               36.5                                      R8     -172.838                                                                                  3.000                                                        R9     -22.950                                                            L5                     2.695         1.741                                                                               27.8                                      R10    -276.177                                                                                  0.720                                                        R11    -76.849                                                            L6                     6.081         1.757                                                                               47.7                                      R12    -19.800                                                                                      2.000-0.20                                                R13    51.599                                                             L7                     3.000         1.847                                                                               23.8                                      R14    31.353                                                                                    2.332                                                        R15    82.914                                                             L8                     7.000         1.800                                                                               42.3                                      R16    -25.647                                                            L9                     3.00                                                         R17    -57.034                  1.805                                                                               25.5                                 ______________________________________                                          BFL = 40.5                                                                     The aperture stop is located 10.73mm after element L3. The space between       Groups IV and V varies as shown for close focus compensation at a linear       rate as the lens focuses to 230.1mm. The entire lens also shifts for           focusing.                                                                

Table 7 sets forth data on lens 16 of FIG. 9 scaled to an EFL of 35.0mm for a 24 × 36mm image frame, and a relative aperture of F/1.9.

                  TABLE VII                                                        ______________________________________                                         FIG. 9                                                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       1598.84mm                                                        L1                       4.160mm     1.750                                                                               35.0                                      R2     -175.71                                                                                    .300                                                        R3     22.57                                                              L2                     2.985         1.487                                                                               70.4                                      R4     13.99                                                                                     9.079                                                        R5     23.40                                                              L3                     5.005         1.700                                                                               47.8                                      R6     15.49                                                                                     8.869                                                        R7     58.80                                                              L4                     3.200         1.831                                                                               36.5                                      R8     -100.28                                                                                   2.385                                                        R9     -24.54                                                             L5                     2.358         1.741                                                                               27.8                                      R10    -845.99                                                                                    6.80                                                        R11    -102.81                                                            L6                     6.778         1.757                                                                               47.7                                      R12    -19.97                                                                                    0.91-3.66                                                    R13    58.83                                                              L7                     3.000         1.847                                                                               23.8                                      R14    32.65                                                                                     1.700                                                        R15    65.28                                                              L8                     7.300         1.800                                                                               42.3                                      R16    -27.00                                                             L9                     0             1.805                                                                               25.5                                      R17    -79.24                                                             ______________________________________                                          BFL = 39.48 - 45.28mm as lens is focused from infinity to 221.3mm. The         aperture stop is located 7.54mm after element L3. The BFL varies from          39.48mm to 45.28mm as the lens is focused from infinity to 221.3mm. The        spacing between Groups IV and V also varies as shown.  221.3             

Table VIII sets forth data on lens 17 of FIG. 10 scaled to an EFL of 35.0mm for a 24 × 36mm image frame, and a relative aperture of F/1.9.

                  TABLE VIII                                                       ______________________________________                                         FIG. 10                                                                                               Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             N.sub.d                              ______________________________________                                              R1     30.600                                                             L1                     7.000         1.487                                                                               70.4                                      R2     170.290                                                                                    .300                                                        R3     34.231                                                             L2                     2.985         1.487                                                                               70.4                                      R4     11.567                                                                                    6.000                                                        R5     67.235                                                             L3                     2.000         1.569                                                                               56.0                                      R6     25.201                                                                                    6.171                                                        R7     46.077                                                             L4                     3.200         1.806                                                                               40.7                                      R8     -644.608                                                                                  7.931                                                        R9     -34.424                                                            L5                     2.358         1.762                                                                               26.6                                      R10    -829.911                                                                                  1.350                                                        R11    -47.763                                                            L6                     4.832                                                        R12    -19.289                  1.757                                                                               47.7                                                          4.70-.10                                                   R13    41.514                                                             L7                     3.000         1.667                                                                               33.1                                      R14    35.544                                                                                    1.900                                                        R15    64.725                                                             L8                     8.000         1.717                                                                               48.0                                      R16    -22.414                                                            L9                     2.700         1.805                                                                               25.5                                      R17    -56.648                                                            ______________________________________                                          The BFL varies from 39.56mm to 44.16mm as the lens is focused from             infinity to 258mm, and the spacing between Groups IV and V varies as           shown. The aperture stop is located 1.59mm behind element L4.            

Table IX sets forth data on a lens substantially as shown in FIG. 7 scaled to an EFL of 28.5mm for a 24 × 36mm frame size and a relative aperture of F/1.9.

                  TABLE IX                                                         ______________________________________                                         FIG. 7                                                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     54.600                                                             L1                     5.700         1.487                                                                               70.4                                      R2     937.48                                                                                     .300                                                        R3                28.640                                                  L2                     2.800         1.487                                                                               70.4                                      R4     11.392                                                                                    4.474                                                        R5     28.640                                                             L3                     2.000         1.517                                                                               64.2                                      R6     15.990                                                                                    13.502                                                       R7     41.450                                                             L4                     3.200         1.689                                                                               31.2                                      R8     840.70                                                                                    3.342                                                        R9     -70.750                                                            L5                     2.164         1.805                                                                               25.5                                      R10    106.030                                                                                   1.900                                                        R11    -71.649                                                            L6                     4.549         1.804                                                                               46.5                                      R12    -21.220                                                                                     4.098-.10                                                  R13    48.140                                                             L7                     2.700         1.741                                                                               27.8                                      R14    35.430                                                                                    1.212                                                        R15    53.960                                                             L8                     9.159         1.639                                                                               55.5                                      R16    -20.430                                                            L9                     2.700         1.805                                                                               25.5                                      R17    -44.190                                                            ______________________________________                                          The aperture stop is located 11.5mm behind L3, Groups V and VI move from       BFL of 39.2mm to 43.2mm for focusing from infinity to 203mm while Groups       - IV are fixed with respect to the film plane.                           

FIGS. 11 and 12 exemplify further comparison of the focal plane shift of the lens of FIG. 8 and the lens of the previously mentioned patent at a magnification of M = - 0.025 for a half image height of 20mm, for both sagittal S and tangential T rays.

The curves of FIG. 11 are relatively close together evidencing substantially less astigmatism than FIG. 12. The curves of FIG. 11, particularly in the saggital have less deviation from the vertical, evidencing reduction in field curvature.

As previously mentioned, the contribution of each lens group to an overall lens is incapable of precise definition since properties of one or more elements and groups serve the same function and are complimenting and supplementing each other. However, in the new lens form described, Group IV is designed to provide certain contributions to the overall lens.

Group IV provides a substantial correction for the Petzval sum of the lens. The axial spacing of the front and rear surfaces contributes to correction of field curvature convex toward the object. Additionally, it provides positive power required to shorten the EFL of the overall lens while maintaining the required back focal length (BFL) to make the lens of the retrofocus type. The EFL of Group IV (F₄) should have the following relation to the EFL of the overall lens (F_(o)).

    2.5 F.sub.o ≦ F.sub.4 ≦ 6.5 F.sub.o

The foregoing is a critical relation, and other preferred relationships exist which do not have the same criticality. The radius R_(r4) of the rear surface is less than F_(o), or

    F.sub.o > R.sub.r4

This relationship contributes to correction for distortion. The axial separation D₄ between front and rear surfaces is a substantial percentage of the EFL of the lens and preferably is in the range of

    0.4 F.sub.o ≧ D.sub.4 ≧ 0.20 F.sub.o

Additionally, to maintain the desired power contribution the combined EFL of Groups III and IV (F₃₄) is preferably

    2.0 F ≧ F.sub.34 ≧ 1.0 F.sub.o

As shown Group IV may be a single element or a doublet, either cemented or air spaced. It might also be defined in three elements. The front surface of Group III, L4, is convex. However, the rear surface may be other than convex depending on the design.

Groups V and VI are of positive power of a magnitude determined by the power of the other elements but in the preferred designs have an EFL (F₅₆)

    4.0 ≧ f.sub.56 ≧ 1.0

while the EFL (F₆) of Group VI is

    2.0 > F.sub.6 ≧ 1.0

group III is of positive power to supplement the positive power of Group IV and preferably has an EFL (F₃) range

    2.5 ≧ F.sub.3 ≧ 1.2F.sub.o

The ranges set forth above may be better appreciated in consideration with Table X which tabulates the ratio of the EFL of each group and combinations thereof to the overall EFL of the lens.

                                      TABLE X                                      __________________________________________________________________________     RATIO OF EFL OF LENS GROUPS TO EFL OF LENS                                          GROUP                                                                               GROUP                                                                               GROUP                                                                               GROUP                                                                               GROUP                                                                               GROUP                                                                               GROUPS                                                                               GROUPS                                                                               GROUPS                          TABLE                                                                               I    II   III  IV   V    VI   V & VI                                                                               I - IV                                                                               III & IV                        __________________________________________________________________________     I    -11.541                                                                             -2.740                                                                              1.472                                                                               3.299                                                                               -2.124                                                                              1.4139                                                                              3.610 1.502 1.261                           II   -10.770                                                                             -2.514                                                                              1.598                                                                               3.492                                                                               -2.307                                                                              1.373                                                                               3.030 1.730 1.332                           III  -9.415                                                                              -2.105                                                                              1.478                                                                               3.410                                                                               -2.276                                                                              1.394                                                                               3.251 1.688 1.249                           IV   -2.602                                                                              -2.391                                                                              1.285                                                                               5.325                                                                               -3.647                                                                              1.492                                                                               2.413 2.414 1.249                           V    -2.282                                                                              -2.656                                                                              2.088                                                                               3.132                                                                               -13.743                                                                             1.854                                                                               2.178 3.202 1.446                           VI   -15.020                                                                             -2.345                                                                              1.414                                                                               4.604                                                                               -2.866                                                                              1.250                                                                               2.103 2.172 1.312                           VII  -3.718                                                                              -2.472                                                                              1.279                                                                               3.342                                                                               -3.061                                                                              1.324                                                                               2.279 2.094 1.121                           VIII -2.799                                                                              -2.052                                                                              1.518                                                                               3.732                                                                               -13.175                                                                             1.381                                                                               1.574 4.829 1.313                           IX   -2.429                                                                              -2.589                                                                              2.200                                                                               2.952                                                                               -6.933                                                                              1.662                                                                               2.179 3.190 1.459                           __________________________________________________________________________

The lenses disclosed may be focused on an object as close as 6.25 EFL's or less than seven inches in the case of the lens of Table IV. In the case of the lens of Table I, the lens is focused to 6.37 EFL or 7.02 inches with minimal astigmatism and field curvature, as exemplified in FIG. 4.

Table XI exemplifies the close focusing capability of the various lens disclosed.

                  TABLE XI                                                         ______________________________________                                         LENS      CLOSE FOCUS DISTANCE (FD)                                                                            FD/.sub.EFL                                    ______________________________________                                         TABLE  I        178mm       7.02 in.  6.20                                            II     178          7.02       6.20                                            III    178          7.02       6.20                                            IV     175          6.91       6.14                                            V      203          7.99       7.12                                            VI     230          9.06       6.57                                            VII    221          8.70       6.31                                            VIII   258          10.20      7.37                                            IX     203          7.99       7.12                                     ______________________________________                                    

It may thus be seen that the objects of the invention set forth above as well as those made apparent are efficiently attained. The invention provides a new wide-angle lens of the retrofocus type having a large relative aperture which will focus to an object distance of less than seven EFL's with minimal astigmatism and field curvature.

While preferred embodiments of the invention have been set forth for purposes of disclosure, other embodiments and modification to the disclosed embodiment of the invention may be derived by others skilled in the art. Accordingly, the appended claims are intended to cover all embodiments and applications of the invention and reversals thereof which do not depart from the spirit and scope of the invention. 

What is claimed is:
 1. A lens of the retrofocus type which comprises a plurality of lens elements arranged in six groups along a common optical axis from the object end to the image end as follows: a first group of negative power including positive and negative lens element, a second negative group in the form of a meniscus having a concave image side surface, a third positive group having a convex object side surface, a fourth positive group having a concave object side surface and convex image side surface, a fifth negative group consisting of a meniscus having a convex object side surface, and a sixth positive group consisting of a biconvex doublet.
 2. The lens of claim 1 further defined by

    6.5 F.sub.o ≧ F.sub.4 ≧ 2.5F.sub.o

where F_(o) is the equivalent focal length of the overall lens, and F₄ is the equivalent focal length of the fourth group.
 3. The lens of claim 1 further defined by

    1.5 F.sub.o ≧ F.sub.34 ≧ 1.0 F.sub.o

where F₃₄ is the combined equivalent focal length of the third and fourth groups, and F_(o) is the equivalent focal length of the overall lens.
 4. The lens of claim 1 further defined in that the first surface of said fourth group is concave and the distance D₄ between the first and last surface thereof is

    0.45 F.sub.o ≧ D.sub.4 ≧ 0.20 F.sub.o

where F_(o) is the equivalent focal length of the overall lens.
 5. The lens of claim 1 further defined by

    2.0 F.sub.o ≧ F.sub.6 ≧ 1.0 F.sub.o

where F_(o) is the equivalent focal length of the overall lens and F₆ is the equivalent focal length of the sixth group.
 6. The lens of claim 1 further defined by

    2.5 F.sub.o ≧ F.sub.3 ≧ 1.2 F.sub.o

where F₃ is the equivalent focal length of said third group, and F_(o) is the equivalent focal length of the overall lens.
 7. The lens of claim 1 further defined by

    5.5 F.sub.o ≧ F.sub.4 ≧ 2.5 F.sub.o

where F₄ is the equivalent focal length of said fourth group and F_(o) is the equivalent focal length of the overall lens.
 8. The lens of claim 1 defined by substantially the following data as scaled to an equivalent focal length of 28.7mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       38.387mm                                                         L1                       2.435mm     1.5168                                                                              64.2                                      R2     18.755                                                                                    8.5083                                                       R3     -119.389                                                           L2                     7.167         1.7995                                                                              42.3                                      R4     -52.877                                                                                      4.72-0.20                                                 R5     18.178                                                             L3                     2.180         1.5831                                                                              59.5                                      R6     12.456                                                                                    9.369                                                        R7     49.0379                                                            L4                     2.159         1.8306                                                                              36.5                                      R8     -123.776 -                    2.581                                     R9     -22.141                                                            L5                     6.000         1.7470                                                                              27.5                                      R10    -109.562                                                           L6                     5.774         1.7620                                                                              40.3                                      R11    -21.131                                                                                   0.135                                                        R12    55.725                                                             L7                     2.454         1.8467                                                                              23.8                                      R13    26.386                                                                                    2.239                                                        R14    76.751                                                             L8                     6.000         1.8042                                                                              46.5                                      R15    -22.374                                                            L9                     1.500         1.8052                                                                              25.5                                      R16    -54.363                                                            ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1, L2; L3; L4; L5, L6, L7; and L8, L9; R1-R16 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 9. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.7mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       38.570mm                                                         L1                       2.435mm     1.5168                                                                              64.2                                      R2     19.187                                                                                    8.508                                                        R3     -118.121                                                           L2                     4.797         1.7995                                                                              42.3                                      R4     -53.498                                                                                      4.000-0.25                                                R5     18.556                                                             L3                     2.180         1.5831                                                                              59.5                                      R6     12.336                                                                                    10.615                                                       R7     50.120                                                             L4                     2.159         1.8306                                                                              36.5                                      R8     -160.5232                                                                                 2.581                                                        R9     -22.590                                                            L5                     10.883        1.7600                                                                              47.5                                      R10    -21.050                                                                                   0.135                                                        R11    51.8954                                                            L6                     3.257         1.8467                                                                              23.8                                      R12    26.298                                                                                    2.239                                                        R13    77.064                                                             L7                     7.000         1.8042                                                                              46.5                                      R14    -18.570                                                            L8                     1.500         1.8052                                                                              25.5                                      R15    -51.214                                                            ______________________________________                                    

where L1-L8 are successive lens elements arranged in six groups L1, L2; L3; L4; L5; L6; L7, L8; R1-R15 are the radii of curvature of the successive lens surfaces according to the sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe numbers, respectively, of the elements L1-L8.
 10. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.7mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       39.897mm                                                         L1                       2.435mm     1.520                                                                               65.6                                      R2     19.832                                                                                    8.500                                                        R3     -111.180                                                           L2                     5.835         1.802                                                                               47.5                                      R4     -55.111                                                                                      4.000-0.25                                                R5     17.557                                                             L3                     2.180         1.807                                                                               44.3                                      R6     12.193                                                                                    10.789                                                       R7     47.013                                                             L4                     2.433         1.833                                                                               41.8                                      R8     -138.976                                                                                  3.390                                                        R9     -23.286                                                            L5                     9.700         1.837                                                                               51.9                                      R10    -21.573                                                                                   0.135                                                        R11    51.904                                                             L6                     3.324         1.848                                                                               23.4                                      R12    26.009                                                                                    2.682                                                        R13    85.346                                                             L7                     1.000         1.848                                                                               23.4                                      R14    31.429                                                             L8                     4.000         1.776                                                                               50.6                                      R15    -43.746                                                            ______________________________________                                    

where L1-L8 are successive lens elements arranged in six groups, L1, L2; L3; L4; L5; L6; L7, L8; R1-R15 are the radii of curvature of the successive lens surfaces according to the sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe numbers, respectively, of the elements L1-L8.
 11. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.5mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     155.101                                                            L1                     4.160         1.562                                                                               58.52                                     R2     -541.744                                                                                   .300                                                        R3     29.242                                                             L2                     3.000         1.487                                                                               70.4                                      R4     13.031                                                                                    12.759                                                       R5     22.898                                                             L3                     2.000         1.800                                                                               42.3                                      R6     15.520                                                                                    8.692                                                        R7     48.249                                                             L4                     3.200         1.785                                                                               25.7                                      R8     -70.561                                                                                   1.967                                                        R9     -24.204                                                            L5                     2.164         1.805                                                                               25.5                                      R10    -1430.264                                                                                  .844                                                        R11    -94.529                                                            L6                     5.504         1.800                                                                               42.3                                      R12    -19.767                                                                                      3.550-1.028                                               R13    45.215                                                             L7                     2.580         1.847                                                                               23.8                                      R14    29.179                                                                                    1.700                                                        R15    70.687                                                             L8                     8.00          1.743                                                                               49.2                                      R16    -19.969                                                            L9                     2.700         1.847                                                                               23.8                                      R17    -44.577                                                            ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 12. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.6mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     42.160                                                             L1                     5.700         1.487                                                                               70.4                                      R2     384.104                                                                                    .300                                                        R3     35.935                                                             L2                     2.800         1.487                                                                               70.4                                      R4     11.488                                                                                    4.032                                                        R5     26.721                                                             L3                     2.000         1,517                                                                               64.2                                      R6     15.510                                                                                    14.343                                                       R7     39.692                                                             L4                     3.200         1.689                                                                               31.2                                      R8     925.392                                                                                   2.973                                                        R9     -76.847                                                            L5                     2.164         1.847                                                                               23.8                                      R10    97.091                                                                                    1.750                                                        R11    -75.162                                                            L6                     4.549         1.800                                                                               42.3                                      R12    -21.352                                                                                      4.098-.100                                                R13    37.634                                                             L7                     2.700         1.722                                                                               29.2                                      R14    32.248                                                                                    2.000                                                        R15    70.613                                                             L8                     8.400         1.641                                                                               59.8                                      R16    -18.940                                                            L9                     2.700         1.805                                                                               25.5                                      R17    -42.358                                                            ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 13. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 35.0mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     31.195                                                             L1                     2.998         1.517                                                                               64.2                                      R2     20.569                                                                                    7.074                                                        R3     -96.642                                                            L2                     2.829         1.785                                                                               25.7                                      R4     -58.277                                                                                   0.726                                                        R5     18.356                                                             L3                     4.321         1.723                                                                               38.0                                      R6     12.649                                                                                    11.925                                                       R7     53.996                                                             L4                     2.800         1.831                                                                               36.5                                      R8     -172.838                                                                                  3.000                                                        R9     -22.950                                                            L5                     2.695         1.741                                                                               27.8                                      R10    -276.177                                                                                  0.720                                                        R11    -76.849                                                            L6                     6.081         1.757                                                                               47.7                                      R12    -19.800                                                                                      2.000-0.20                                                R13    51.599                                                             L7                     3.000         1.847                                                                               23.8                                      R14    31.353                                                                                    2.332                                                        R15    82.914                                                             L8                     7.000         1.800                                                                               42.3                                      R16    -25.647                                                            L9                     3.000                                                        R17    -57.034                  1.805                                                                               25.5                                 ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 14. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 35.0mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius     Between Surfaces                                                                             N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1       598.84mm                                                         L1                       4.160mm     1.750                                                                               35.0                                      R2     -175.71                                                                                    .300                                                        R3     22.57                                                              L2                     2.985         1.487                                                                               70.4                                      R4     13.99                                                                                     9.079                                                        R5     23.40                                                              L3                     5.005         1.700                                                                               47.8                                      R6     15.49                                                                                     8.869                                                        R7     58.80                                                              L4                     3.200         1.831                                                                               36.5                                      R8     -100.28                                                                                   2.385                                                        R9     -24.54                                                             L5                     2.358         1.741                                                                               27.8                                      R10    -845.99                                                                                    .680                                                        R11    -102.81                                                            L6                     6.778         1.757                                                                               47.7                                      R12    -19.97                                                                                    0.91-3.66                                                    R13    58.83                                                              L7                     3.000         1.847                                                                               23.8                                      R14    32.65                                                                                     1.700                                                        R15    65.28                                                              L8                     7.300         1.800                                                                               42.3                                      R16    -27.00                                                             L9                     0             1.805                                                                               25.5                                      R17    -79.24                                                             ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 15. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 35.0mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             N.sub.d                              ______________________________________                                              R.sub.1                                                                               30.600                                                             L1                     7.000         1.487                                                                               70.4                                      R2     170.290                                                                                    .300                                                        R3     34.231                                                             L2                     2.985         1.487                                                                               70.4                                      R4     11.567                                                                                    6.000                                                        R5     67.235                                                             L3                     2.000         1.569                                                                               56.0                                      R6     25.201                                                                                    6.171                                                        R7     46.077                                                             L4                     3.200         1.806                                                                               40.7                                      R8     -644.608                                                                                  7.931                                                        R9     -34.424                                                            L5                     2.358         1.762                                                                               26.6                                      R10    -829.911                                                                                  1.350                                                        R11    -47.763                                                            L6                     4.832                                                        R12    -19.289                  1.757                                                                               47.7                                                          4.70-.10                                                   R13    41.514                                                             L7                     3.000         1.667                                                                               33.1                                      R14    35.544                                                                                    1.900                                                        R15    64.725                                                             L8                     8.000         1.717                                                                               48.0                                      R16    -22.414                                                            L9                     2.700         1.805                                                                               25.5                                      R17    -56.648                                                            ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5, L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 16. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.5mm.

    ______________________________________                                                                Axial Distance                                          Lens        Radius(mm) Between Surfaces(mm)                                                                         N.sub.d                                                                             V.sub.d                              ______________________________________                                              R1     54.600                                                             L1                     5.700         1.487                                                                               70.4                                      R2     937.48                                                                                     .300                                                        R3     28.640                                                             L2                     2.800         1.487                                                                               70.4                                      R4     11.392                                                                                    4.474                                                        R5     28.640                                                             L3                     2.000         1.517                                                                               64.2                                      R6     15.990                                                                                    13.502                                                       R7     41.450                                                             L4                     3.200         1.689                                                                               31.2                                      R8     840.70                                                                                    3.342                                                        R9     -70.750                                                            L5                     2.164         1.805                                                                               25.5                                      R10    106.030                                                                                   1.900                                                        R11    -71.649                                                            L6                     4.549         1.804                                                                               46.5                                      R12    -21.220                                                                                     4.098-.10                                                  R13    48.140                                                             L7                     2.700         1.741                                                                               27.8                                      R14    35.430                                                                                    1.212                                                        R15    53.960                                                             L8                     9.159         1.639                                                                               55.5                                      R16    -20.430                                                            L9                     2.700         1.805                                                                               25.5                                      R17    -44.190                                                            ______________________________________                                    

where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N_(d) and V_(d) are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.
 17. the lens of claim 1 further defined by

    1.5 F.sub.o ≧ F.sub.34 ≧ 1.0 F.sub.o

where F₃₄ is the combined equivalent focal length of the third and fourth groups, and F_(o) is the equivalent focal length of the overall lens.
 18. The lens of claim 2 further defined in that the axial distance D₄ between the first and last surface of said fourth group is

    0.45 F.sub.o ≧ D.sub.4 ≧ 0.20 F.sub.o

where F_(o) is the equivalent focal length of the overall lens.
 19. The lens of claim 2 further defined by

    2.5 F.sub.o ≧ F.sub.3 ≧ 1.2 F.sub.o

where F₃ is the equivalent focal length of said third group, and F_(o) is the equivalent focal length of the overall lens.
 20. The lens of claim 2 further defined by

    2.0 F.sub.o ≧ F.sub.6 ≧ 1.0 F.sub.o

where F_(o) is the equivalent focal length of the overall lens and F₆ is the equivalent focal length of the sixth group.
 21. The lens of claim 1 further defined by

    6.5 F.sub.o ≧ F.sub.4 ≧ 2.5 F.sub.o and

    1.5 F.sub.o ≧ F.sub.34 ≧ 1.0 F.sub.o

where F₄ is the equivalent focal length of said fourth group, F₃₄ is the combined equivalent focal length of said third and fourth groups and F_(o) is the equivalent focal length of the overall lens.
 22. A retrofocus lens consisting of nine elements and from the object side comprising a first two element group including a positive and a negative lens element of overall negative power, a third element in the form of a negative meniscus having a convex object side surface, a fourth positive element having a convex object side surface, fifth and sixth elements, said fifth element having a concave object side surface and said sixth element having a convex image side surface, said fifth and sixth elements being of overall positive power, a seventh element in the form of a negative meniscus having a convex object side surface, and eighth and ninth elements cemented together and being overall bi-convex.
 23. The lens of claim 22 further defined by

    1.5 F.sub.o ≧ F.sub.34 ≧ 1.0 F.sub.o

where F₃₄ is the combined equivalent focal length of the third and fourth groups, and F_(o) is the equivalent focal length of the overall lens.
 24. The lens of claim 22 further defined in that the axial distance D₄ between the first and last surface of said fourth group is

    0.45 F.sub.o ≧ D.sub.4 ≧ 0.20 F.sub.o

where F_(o) is the equivalent focal length of the overall lens.
 25. The lens of claim 22 further defined by

    2.5 F.sub.o ≧ F.sub.3 ≧ 1.2 F.sub.o

where F₃ is the equivalent focal length of said third group, and F_(o) is the equivalent focal length of the overall lens.
 26. The lens of claim 22 further defined by

    2.0 F.sub.o ≧ F.sub.6 ≧ 1.0 F.sub.o

where F_(o) is the equivalent focal length of the overall lens and F₆ is the equivalent focal length of the sixth group.
 27. A retrofocus lens consisting of eight elements and from the object side comprising a first two element group including a positive and negative lens element of overall negative power, a third element in the form of a negative meniscus having a convex object side surface, a fourth positive element having a convex object side surface, a fifth positive element having a concave object side surface and a convex image side surface, a sixth element in the form of a negative meniscus having a convex object side surface, and seventh and eighth elements cemented together and being overall bi-convex.
 28. A lens of the retrofocus type which comprises from the object end a first group of a positive and a negative element of overall negative power, a second group of negative power in the form of a meniscus having a concave image side, a third group of positive power having a convex object side surface, a fourth positive group comprising two elements and having a concave object side and a convex image side, a fifth group and a sixth group, said fifth group consisting of a negative meniscus having a convex object side surface, said sixth group consisting of a biconvex doublet.
 29. The lens of claim 28 further defined by

    1.5 F.sub.o ≧ F.sub.34 ≧ 1.0 F.sub.o

where F₃₄ is the combined equivalent focal length of the third and fourth groups, and F_(o) is the equivalent focal length of the overall lens.
 30. The lens of claim 28 further defined in that the axial distance D₄ between the first and last surface of said fourth group is

    0.45 F.sub.o ≧ D.sub.4 ≧ 0.20 F.sub.o

where F_(o) is the equivalent focal length of the overall lens.
 31. The lens of claim 28 further defined by

    2.5 F.sub.o ≧ F.sub.3 ≧ 1.2 F.sub.o

where F₃ is the equivalent focal length of said third group, and F_(o) is the equivalent focal length of the overall lens.
 32. The lens of claim 28 further defined by

    2.0 F.sub.o ≧ F.sub.6 ≧ 1.0 F.sub.o

where F_(o) is the equivalent focal length of the overall lens and F₆ is the equivalent focal length of the sixth group.
 33. The lens of claim 28 further defined by

    1.5 F.sub.o ≧ F.sub.34 ≧ 1.0 F.sub.o

    0.45 F.sub.o ≧ D.sub.4 ≧ 0.20 F.sub.o

    2.5 F.sub.o ≧ F.sub.3 ≧ 1.2 F.sub.o

    2.0 F.sub.o ≧ F.sub.6 ≧ 1.0 F.sub.o

where F_(o) is the equivalent focal length of the overall lens, F₃₄ is the combined equivalent focal length of the third and fourth groups, D₄ is the axial distance between the front and rear surfaces of the fourth group, F₃ is the equivalent focal length of the third group, and F₆ is the equivalent focal length of the sixth group. 